The present invention relates generally to electrical circuit interrupting means, and more particularly, to a new and improved expulsion type fuse cutout fuseholder structural assembly which, in addition to being capable of achieving interruptions under low fault current conditions, can also in fact, achieve high fault current interruptions so as to provide a fuse cutout with an interruption rating of 8000 amps within a 38 KV fuse cutout.
In connection with the interruption of fault current conditions within an electrical circuit, conventional expulsion type fuse cutout fuseholder structural assemblies rely upon the intense heat of the electric arc, which develops as a result of the rupture of the fuse link, to vaporize a bone fiber liner, disposed internally of the fuse tube outer covering, into various gases, such as, for example, carbon monoxide, water vapor, methane, hydrogen, and the like, whereby such evolved gases serve to expurgate the entire interior bore of the fuse tube assembly and thereby provide the entire interior bore of the fuse tube assembly with an environment within which the arc cannot re-establish itself at and after current zero, a phenomenon known in the art as re-igniting or re-striking. In view of the fact that an arc that persists for several cycles can be extremely damaged to a particular piece of electrical equipment disposed within the circuit, it is operatively mandatory that the aforenoted expurgation of the entire interior bore of the fuse tube assembly be achieved by the first current zero after element melting under both low and high current fault conditions.
Since the aforenoted gases are generated or evolved at a substantially high rate of speed and within a relatively confined area or volume, as defined by means of the interior bore of the fuse tube assembly, substantial pressure is developed internally of the fuse tube assembly, and this pressure is utilized to expel the ionized gases developed within the fuse tube assembly as a result, for example, of the ablation and vaporization of the fuse tube assembly bone fiber liner, as well as, the melting and destruction of the fuse link and the link auxiliary tube, whereby the aforenoted environment within the fuse tube assembly is achieved. The buildup of pressure within the fuse tube assembly, and the subsequent expulsion-venting of the gases from the fuse tube assembly, within an extremely short, relative period of time, however, leads to the development of substantial thrust and reaction forces upon the entire fuse tube assembly. During particular instances of current fault interruption conditions, the magnitude of such forces may reach such a value that portions or components of the fuse tube assembly may be permanently deformed or otherwise damaged. In view of the fact that greater pressures manifest themselves under high current fault conditions, the potential also exists for the rupturing of the fuse tube assembly if excessive pressure levels develop within the fuse tube assembly.
In order to effectively limit the maximum pressure levels and eliminate the potential for the occurance of such aforementioned deleterious effects upon the fuse tube assembly, conventional fuse tube constructions sought to provide the fuse tube assemblies with an interior bore diametrically larger than that of previous fuse tube assembly bores. Such an solution served, however, to increase the interior volume of the fuse tube assembly bore, and therefore effectively reduce the pressure level of a predetermined volume of evolved gas. The surface area of the fuse tube assembly bone fiber liner exposed to the arc generated within the fuse tube assembly is, however, dramatically increased. Consequently, a substantial reduction in relative pressure levels is not in fact achieved. In addition, by increasing the interior diameter of the fuse tube assembly bore, such conventional fuse tube constructions experienced additional operational difficulties in that such fuse tube assemblies were not capable of consistently clearing the circuit at the first curent zero, but, to the contrary, permitted the arcs to persist for several additional cycles. This problem is particularly acute under low current fault conditions in view of the fact that under certain transient conditions, the enlarged fuse tube assembly bore prevented sufficient pressure from developing within the fuse tube assembly so as to expurgate the tube and thereby prevent the re-ignition or re-striking of the arc.
In order to therefore overcome these various operational disadvantages characteristic of high and low current fault conditions, another prior art or conventional fuse tube assembly construction, as exemplified by means of U.S. Pat. No. 3,102,178, issued to Raymond J. Bronikowski, entitled, "Fuse Tube Construction", and assigned to the assignee of the present application, does not increase the relative diametrical size of the fuse tube assembly bore, but to the contrary, incorporates therewithin a conductive sleeve which is disposed interiorly of the fuse tube assembly and interposed between two sections of the fuse tube assembly bone fiber liner. As a result of this particular construction, not only is the interior diametrical bore size of the fuse tube assembly preserved, whereby low current fault interruptions are facilitated as a result of the maintenance of sufficient pressure levels within the fuse tube assembly, but in addition, the volumetric amount of the gas-evolving bone fiber liner is effectively reduced, whereby high current fault interruptions are likewise facilitated in view of the fact that the pressure levels developed within the fuse tube assembly bore are effectively limited.
It may thus be appreciated that the foregoing fuse tube assembly construction performs admirably throughout the low and high fault current ranges, however, several operational disadvantages or drawbacks have become evident as posing potential problems, during actual field site usage, whereby it is not only possible that damage to equipment may be experienced as a result of arc re-ignition or re-striking, but in addition, damage to the fuse tube assembly may likewise be experienced as a result of deformation, distortion, erosion, or ablation of the fuse tube assembly bone fiber liner and conductive sleeve components, as well as a result of the physical separation of the fuse tube assembly bone fiber liner relative to the conductive sleeve and outer covering or wrapping components. For example, it is noted in connection with the embodiment of FIG. 2, of the Bronikowski patent, that the wall thickness dimension of the conductive sleeve component is relatively small, and consequently, during high current fault conditions, ablation or erosion of the sleeve can eliminate the serviceability of the conductive sleeve, or substantialy reduce its service life. It should also be noted at this juncture, that while the conductive sleeves employed within the embodiments of FIGS. 3 and 4, of the Bronikowski patent, exhibit portions which have thickness dimensions which are relatively large, or at least substantially greater than the corresponding radial thickness dimension characteristic of the embodiment of FIG. 2, the conductive sleeves of the embodiments of FIGS. 3 and 4, are exposed to the environment external to the fuse tube assembly, whereby the potentially undesirable conditions facilitating flashover are present.
Continuing still further, in view of the fact that within all of the structural embodiments of the Bronikowski patent, there is no integral or fixed structural interconnection defined between the bone fiber liner and the outer covering or wrapping, or similarly between the bone fiber liner and the conductive sleeve, the gases evolved from the bone fiber liner tend to be thrust between the end surfaces of the bone fiber liner and the conductive sleeve (which are in simple butt contact with each other), as well as behind the conductive sleeve, under the pressurized conditions existing within the fuse tube assembly bore. As a result of such pressurized gaseous thrust forces acting upon the conductive sleeve, the sleeve tends to be distorted or deformed, or separated from the bone fiber liner and outer covering or wrapping. These conditions are, of course, entirely undesirable in that the conductive sleeve may tend to become jammed within the fuse tube assembly bore, or at least substantially block the same, thereby preventing the desirably required pressurized evacuation of the bone fiber liner gases from the fuse tube assembly bore. Such an operational failure of the fuse tube assembly can also lead to rupturing or bursting of the fuse tube assembly, or damage to other components of the entire fuseholder assembly, and in addition, in view of the fact that the interior environment of the fuse tube assembly has not been properly and completely expurgated, arcing within the circuit may continue to persist.
Accordingly, it is an object of the present invention to provide a new and improved expulsion type fuse cutout fuseholder structural assembly.
Another object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which overcomes the various disadvantages and operational drawbacks characteristic of prior art or conventional expulsion type fuse cutout fuseholder structural assemblies.
Yet another object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which, in addition to properly performing electrical line or circuit interruptions under low current fault conditions, can also properly perform electrical line or circuit interruptions under high current fault conditions.
Still another object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly with an interruption rating which is substantially greater or higher than prior art or conventional expulsion type fuse cutout fuseholder structural assemblies.
Yet still another object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which provides for the integral interconnection defined between the fuse tube assembly bone fiber liner and the sleeve insert, as well as the integral interconnection defined between the fuse tube assembly bone fiber liner and the outer covering or wrapping.
Still yet another object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which provides for the integral interconnection defined between the fuse tube assembly sleeve insert and the outer covering or wrapping, while maintaining the sleeve insert housed entirely interiorly within the outer covering or wrapping.
A further object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which effectively limits the pressurization levels developed internally within the fuse tube assembly under high current fault conditions, while permitting sufficient pressurization levels to develop internally within the fuse tube assembly under low current fault conditions, whereby desirable electrical line or circuit interruptions can, in fact, be properly achieved both under low and high current fault conditions.
A yet further object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly wherein the fuse tube assembly bone fiber liner, the fuse tube assembly sleeve insert, and the outer covering or wrapping components are integrally connected together so as to enhance the structural integrity of the fuse tube assembly, whereby the fuse tube assembly can effectively withstand the increased pressurization levels developed internally within the fuse tube assembly attendant high current fault conditions without distortion or rupture of the fuse tube assembly or any of its components, and thereby exhibit a higher interruption rating than is capable of currently being achieved with conventional fuse cutout fuseholder structural assemblies.
A still further object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly wherein the fuse tube assembly bone fiber liner is integrally connected to the fuse tube assembly sleeve insert, as well as to the outer covering or wrapping, whereby the tendency of separation, distortion, deformation, or the like, of the fuse tube assembly bone fiber liner relative to the fuse tube assembly sleeve insert and the outer covering or wrapping under high pressurization conditions is effectively counterbalanced.
A yet still further object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly wherein the fuse tube assembly is provided with sufficient radial wall thickness so as to effectively counteract the tendency for the fuse tube assembly sleeve insert to undergo ablation or erosion under high current fault conditions, while, nevertheless, being retained entirely interiorly within the fuse tube assembly outer covering or wrapping so as to eliminate any potentially dangerous flashover conditions from developing.
A still yet further object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly wherein the fuse tube assembly sleeve insert is provided with sufficient radial wall thickness so as to effectively counteract any tendency for the fuse tube assembly sleeve insert to undergo ablation or erosion under high current fault conditions, and is housed entirely internally within the fuse tube assembly outer covering or wrapping, however, the diametrical extent of the fuse tube assembly bore has a value which is comparable to conventional fuse tube asesmbly bores so as not to adversely affect low and high current fault interruption capabilities of the fuse tube assembly.
An additional object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which exhibits enhanced structural integrity, whereby in accordance with accepted industry standards, the assembly can successfully clear the maximum rating of the cutout assembly a minimum of three successive times, and subsequent to the third such interruption, nevertheless, remain capable of carrying the rated value of continuous current.
A yet additional object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which exhibits enhanced structural integrity, whereby even under high current fault conditions, the structural assembly will remain intact and not exhibit disruptive plastic deformation or distortion requiring extensive replacement of component parts or even the entire fuse cutout fuseholder structural assembly.
A still further additional object of the present invention is to provide a new and improved expulsion type fuse cutout fuseholder structural assembly which can be economically manufactured.